Prior methods and technology having to do with killing bacteria in meat include the application of chemicals, e.g. ethyl alcohol; the application of live steam to the meat surface; and the application of radiation, especially hard gamma radiation. The application of chemicals such as alcohol has the disadvantage of being effective only as regards the surface bacteria, and possibly altering the taste of the meat. Live steam undesirably changes the color of the surface of the meat, turning it to a brownish color, and in any event has limited penetration. Radiation will kill all of the bacteria on and in the meat without altering the appearance of the meat, but some of the molecules of the meat are altered by radiation, with resultant fear that this alteration may produce undesirable effects, e.g. cancer, in humans; moreover, radiation is simply not presently accepted by the U.S. public.
Most bacteria occurs naturally only on the meat surface. With most forms of cooking, heat is applied to the meat surface, and through conduction is transferred throughout the meat. Experience has shown that the meat surface becomes hot enough in most instances to kill the bacteria, but in many cases the inside of the meat does not reach a microorganism killing temperature. With unground meat, e.g. steaks, this is normally not a problem, because the inner portion of the meat is likely to be bacteria-free. However, with ground meat the bacteria from the surface is distributed throughout the meat. Thus, the largest problem with bacteria occurs with ground meat, and there have been some recent occurrences of pathogenic E-Coli bacteria in insufficiently cooked hamburger killing persons who had eaten such hamburgers. Of the three prior methods of killing bacteria mentioned above, only radiation can kill the bacteria within the meat.
Killing microorganisms on and in meat is obviously important from a health standpoint, inasmuch as some of the bacteria can be life-threatening. However, killing all or reducing the amount of bacteria on the meat surface also greatly increases the shelf life of the meat. This is of large economic importance.
U.S. Pat. Nos. 5,328,403 and 5,273,766, both in the name of John B. Long, are directed to the treatment of meat by exposing it to an explosive force. While these patents are primarily directed to the use of such an explosive force in order to tenderize the meat, such an explosive force also kills microorganisms on and in the meat. Experiments conducted on meat using the system of the aforementioned U.S. patents '403 and '766 have shown that about 90% of the surface bacteria on the meat samples were killed. It would, of course, be desirable to increase the percentage of bacteria killed by such a process.